Vacuum tube



\ July 20, 1943. R. c. HERGENROTHER 2,324,776

VACUUM TUBE Filed March 8, 1941 w a N Anode Ourrefif (Milliampen s) 3 Anode Currant (Milliumpereg),

Control -elecirode Poieniiol (Volts) INVENTOR RU LF 5 HERGENROTHER ATTORNEY Patented July 20, 1943 2.324.1 6 VACUUM TUBE Rudolf 0. Bergenrotber, Beecbhurst, N. I, as-

, Ilml to Baseltine Corporation, a corporation of Delaware Application March s, 1941, Serial No. 382,219 11 cum. etc-21.5)

The present invention relates to vacuum tubes and, particularly, to vacuum tubes having a low amplification factor or mu. In greater particularity, the invention relates to low-mu vacuum tubes adapted to deliver relatively high values of output power.

It has heretofore been proposed that a low-mu vacuum tube be provided by inverting a conventional type of triode or pentode vacuum tube, inversion being accomplished by connecting the anode to-serve as the control electrode of the tube and one of the grids to serve as the anode.

may be chosen for use as the anode of the in verted tube has a heat dissipation less than .that or the conventional anode and consequently places a limitation on the maximum power which may be obtained from the tube when used in this inverted manner.

It has also been proposed that the limitation on the power output which results from invert-' ing a conventional vacuum tube be avoided by a rather special tube construction wherein a planar.

anode and planar control electrode are positioned on opposite sides of a cathode. The cathode of I such a tube has heretofore been provided with an electron-emissive surface which is directly exposed to substantially one entire surface of both the anode and the controlelectrode. While this construction provides a low-mu vacuum tube, it v is subject to the limitation that a large portion of the cathode current, that is, the portion which is due to the electron emission on the side of the cathode facing the anode, is not controlled by the control electrode and consequently produces considerable anode dissipation without contributing to the power output of the tube. Additionally, the grid voltage-anode current characteristic of the tube exhibits a substantial tailingoff in the region of large values of negative grid bias and the tube-consequently does not cut off' at any practicable value of control-electrode bias.

It is an object of the invention, therefore, to provide a new and improved vacuum tube of the low-mu type and one which avoids one or more of the above-mentioned disadvantages and limitations of the prior art devices.

It is a further object of the invention to provide a low-mu vacuum tube adapted to provide large power outputs and one having a relatively sharp-cutoff operating characteristic.

In' accordance with one form of the invention, avacuum tube comprises a cathode having an electron-emissive surface over only a portion of the area thereof, an anode supported in spaced opposing relation to thecathode with substantially only the nonemissive surface of the oathode facing toward the anode, and a control electrode supported in spaced opposing relation to both the anode and cathode and outside of the space current path therebetween.

In a particular form of the invention, a vacuum tube of the type described comprises a control electrode positioned on the opposite side of the cathode from the anode, and the cathode has an electron-emissive surface only on the side thereof away from the anode.

In a preferred form of the invention, a vacuum tube of the type described comprises a cathode, a pair of anodes, each of generally hyperbolic configuration and each consisting of anode surface portions which are substantially unexposed to the cathode-emissive surface, and means supporting the anodes in spaced relation to the cathode and on opposite sides thereof with the planes of symmetry of the anode surfaces substantially coincident with each other and including the axis of the cathode. The tube includes a pair of control electrodes, each having a; surface also of generally hyperbolic configuration, and means sup-- porting the control electrodes in spaced relation to the cathode and on opposite sides thereof with the planes of symmetry of the control-electrode surfaces substantially coincident with each other. substantially normal to those of the anodes and including the axis of the cathode.

In another form of the invention, a vacuum tube of the type described comprises a cathode having an electron-emissive surface over only a together with other and further objects thereof,

gram of the Fig. i tube and shows the arrange ment of'the tube electrodes thereof Figs. 3 and 4 represent plots of the equipotentialfields' which are established between the electrodes .of the tube of Fig. 1; Fig. 5 is a graph representing the operating characteristics of a tube of the prior art similar in construction to that of Fig, 1, while Fig. 6 is a graph representing the corresponding operating characteristics of the Fig. 1 tube; Fig. 'i is a cross-sectional view of a tube embodying a modified form of the invention; Figs. 8 and 9 represent equipotential field plots for a tube embodying the Fig. '7 modification of the invention; and Fig. 10 is a cross-sectional view of a vacuum tube embodying an additional modified form of the invention.

Referring now more particularly to Fig. 1 of the drawing, there is shown a view in elevation of a tube embodying one form of the invention. In general, the tube comprises an envelope l0, partly broken away, having a reentrant stem or press ll through which are sealed lead-in conductors l2. The lead-in conductors 12 are connected to individual prongs, not shown, of the tube base 9, and are individually connected to and support a planar anode l3, a plurality of cylindrical cathode members I4, more fully described hereinafter, which are aligned in a plane substantially parallel to that of the anode l3,

and individual heaters, not shown, provided in-' ternally of the cathode members M. A lead-in conductor I5 is sealed through the top of the tube envelope l andsupports a planar control electrode it in spaced opposing relation to both the anode l3 and the cathode members I l and on the opposite side of the cathode members from the anode.

It will be understood that the vacuum tube thus far described involves, with the exception of the cathode members M, a construction heretofore proposed. Referring particularly to Fig. 2, which is a schematic cross-sectional view of the electrode arrangement of the Fig. 1 tube, each of the cathode members It is provided with an electron-emissive coating or surface I! over only a portion of the area thereof and specifically on the side thereof which is exposed to the control electrode I 6. In practice, the electron-emissive coating H is provided only over one-half, or slightly less, of the peripheral surface of the cathodemembers M and on the side of the cathode members opposite to the anode 63. As a result of this construction, substantially all of the surface of the anode I 3 is unexposed to the cathode-emissive surface l'l while the maximum surface of the control electrode l6 faces toward or is exposed to the cathode-emissive surface. Expressed somewhat difierently, it is also true that the anode I3 is supported in spaced opposing relationship to the cathode It and that substantially only the nonemissive surface of the cathode faces toward the anode. The trajectories of the electrons emitted by the electron-emissive surface I! to the anode l3 are indicated in Fig-2 by the dotted lines. Since the electron trajecmember.

Fig. 3 represents a plot of the equipotential field which is established between the several tube elements of the Fig. 1 construction when the control electrode I6 is at the potential of the cathode members l4 so that there is no electrostatic field therebetween. If the anode I3 is energized to some positive potential, there is produced between the anode and cathode an equipotential field, represented by the equipotential lines a--c, inclusive, which extends into close proximity to substantially the entire area of the electronemissive surfaces I! so that the anode current is 5 a maximum.

Fig. 4 represents the corresponding plot of the cquipotential field when the control electrode I6 is energized to a. predetermined negative potential sufiicient to bias the tube to cutoff. In this 10 event, the equipotential field of the control electrode I 6, which is represented by the dashed lines ji, inclusive, extends into. close proximity to substantially the entire area of the electronemissive surfaces l1, thereby to reduce substantially to zero the area of the electron-emissive surfaces over which any of the equipotential field 0f the anode l3 extends into close proximity. Thus, since the electrostatic field in close proximity to the entire area of the electron-emissive surfaces l! is negative, all of the electrons emitted by the electron-emissive surfaces H are returned thereto and none flow to the anode l3 so that the anode current is cut off. It will be evident from the representation of Fig. 4 that the electron emission to the anode portions is,

therefore, substantially terminated by an equipotential field which is produced by the controlelectrode means l6 and which extends around the cathode through a total angle not substantially exceeding 180 degrees.

Fig. 5 is a graph representing typical controlelectrode bias-anode current operating characteristics of a prior art vacuum tube of similar construction but not embodying the present invention. It will be evident that such prior art tubes are distinguished by a long tailing-off of the characteristic in the region of large values of control-electrode bias and are not subject to cutoff with any practicable values thereof.

Fig. 6 is a graph representing corresponding typical operating characteristics of the Fig. 1 vacuum tube. It will be seen from this figure that the tube of Pig. 1 has a definite cutoff characteristic and is quite free from the-tailing-off which is inherent in the characteristics of the prior art tubes of this type.

As illustrative of a specific embodiment of the invention, the following specifications are given for an embodiment of the invention of the type shown in Fig. 1:

4 in number Anode-cathode spacing do 0.060 Control-electrode cathode spacing do 0.120

Amplification factor mu 0.56 to 0.39

Anode potential vo1ts 152 to 107 Anode current milliamperes 100 to 50 Mutual conductance factor (gm) micr0mhos 580 to 130 Anode potential volts 174 to Grid potential do 25 to 200 sectional view of Fig. 7 which is functionally essentially similar to that of Fig. 1,-similar tube elements being designated by similar reference numerals. The tube of Fig. 7 is provided with a pair of anodes 13, or what may be considered portions of a single anode. of generally hyperbolic configuration which are positioned in spaced relation to. and on opposite sides of, the cathode I 4 which is of circular cross-section and is coated over its .entire surface with an electron-emissive material. tions l3a, I3b which are disposed substantially edge-wise toward the cathode ll, whereby the anode surface portions are substantially unexposed to the cathode-emissive surface H. The tube also includes a pair of control electrodes H5, or what may be considered portions of a single control electrode, which have surfaces generally of hyperbolic configuration and are positioned in spaced relation to and on opposite sides of the cathode Hi. It will be, understood that the several tube elements of Fig. 7 are supported by lead-in conductors, not shown, from-the tube envelope in in. a manner essentially similar to that of the Fig. 1 arrangement. It will further be evident that the planes of symmetry of theanode surface portions represented by the traces A. A and B; B are substantially coincident and are normal to the planesof symmetry 0. C and D. D of the control-electrode surfaces which are also substantially coincident with each other and that all of such planes include the axis of the cathode l4.

Fig. 8 represents an equipotential field plot of thefleld-which is established between the anodes l3 and control electrodes l6 when the control electrodes it have the same potential'as the cathin Each of the anodes l3 has surface porode l4. It will'be evident from this figure that a the energization of the anodes ii to a predetermined positive potential produces between the anodes and cathode an equipotential field represented bv the solid-line curves a-'-e, inclusive, which extends into close proximity to substantially the entire area of the cathode-emissi ve surface I! so that the anode current is a maximum.

Fig. 9 represents a similar equipotential field plot under the, condition that the control electrodes iii are biased to a negative potential su'fli ciently large that the tube is cut oil. The equiw potential field existing between the control electrodes l6 and the cathode I4 is represented by the brokeri"-line curves ,f-i, inclusive, of this figure. It will be seen from this figure that the energization of the control electrodes to a predetermined negative potential reduces substantially to zero the area of the cathode-emissive surface llover which any of the equipotential field of the anodes l3 extends into close proximity so that the space current of the tube is substantially cut oif.

If desired, a conventional space-charge grid may surround the cathode l4 and a screen grid may be positioned between the cathode I4 and each of the anodes l3, a conventional suppressor grid being preferably provided in this case between each of such screen grids and the anode individual thereto. The screen grid should .have

a cross-section generally of hyperbolic configuration and the anodes may be simply elongated planar conductive members.

The modification of the invention represented by the cross-sectional view of Fig. 10 is functionally essentially similar to that of Fig. 7,

similar'tube elements being designated by similar v reference numerals. In this case, the anodes ii members having anode'surface portions I30, lld

disposed edgewise to the cathode H, whereby the anode surface portions I30, l3d-are substantially unexposed to the cathode-emissive surfaces ll. The planes of the anodes II are substantially coincident with each other and include theaxlsof the cathode ll. The controlelectrodes l8 also are planar members "and are supported in spaced opposing relation-to both the anodesl3 and the cathode II with the planes of the control electrodes substantially parallel with each other and l with the plane of the anodes. The cathode H is here shown as having a generally elliptical crosssectional configuration and'the electron emissive coatings I! are provided'only on the portions of the cathode which are exposed tov the control electrodes l8.

It will be understood that the anodes 13, control electrodes IB, and cathode l4 are supported from the tube envelope l0 by leadin conductors, not shown, in a manner similar to that of Fig. 1. o o a i The following specifications are illustrative of a specific embodiment of the invention generally Mutual conductance '(gm) y micromhos 110 to 340,

Anode potential volts 81 Control-electrode potential volts l00 to -25 In the foregoing description of the invention,

frequent reference has been made to the unj By the term exposed surface of the anode. unexposed surface as applied to an anode sur-- face in this specification and appended claims is meant either a surface'as to which there is substantially no direct unobstructedpath to the electron-emissive surface of the cathode, as in the Fig. 1 construction, or a surface that is disposed substantially edgewise to the cathode, as

in the construction of Figs. '7 and 10.

In the appended claims, reference is made to anode and control-electrode meanshaving portionsaltern'ately mounted around the cathode of the-tube. By this expression is meant that, in

a path around the cathode. there exists, for example, first a control electrode orcontrol-electrode portion, then an anode oranode portion, then a control electrode or control-electrode portion, etc. This expressionis intended to be applicable to and to describe the electrode arrangement of all of the tube constructions disclosed. i-

It will be evident from theforegoing description of the invention that a tube embodying the present invention is not only capable, of de-- livering appreciable power outputs due to eifec tive anode dissipation, but has the advantage of a relatively sharp cutoff operating characteristic not obtainable in prior art tubes of similar general type.

While there have been described what are at in this modification are a pair of elongated planar a present considered to be the preferred embodiments of this invention, it will be obvious to those .skilled in the art that. various changes and modipath between said anode and said cathode.

flcations may be made therein without departing from the invention, and it is, therefore, aimed 2. A vacuum tube comprising, an evacuated envelope enclosing a cathode having an electronemissive surface over only a portion of the area thereof, an anode supported in spaced opposing relation to said cathode with substantially only the nonemissive surface of said cathode facing toward said anode, and a control electrode supported in spaced opposing relation to both said anode and said cathode and having a continuous conductive surface outside of the space current 3. A vacuumtube comprising, anevacuated envelope enclosing a cathode having an electronemissive surface over only a portion of the area thereof, an anode supported inspaced opposing relation to said cathode with substantially only the nonemissive surface of said cathode facing I toward said anode, and a control electrode supported in spaced opposing relation to both said anode and said cathode with said cathode-emissive surface facing toward said control electrode.

4. A vacuum tube comprising, an evacuated envelope enclosinga cathode having an electronemissive surface over only a portion of the area thereof, an anode supported in spaced opposing relation to said cathode with substantially only the nonemissive surface of said cathode facing toward said anode, and a control electrode supported in opposing relation to both said anode and said cathode and on the opposite side of said cathode from said anode.

. 5. A vacuum tube comprising, a substantially.

planar anode. a cathode comprising a plurality of cathode members supported'in spaced opposing relation to said anode with said members aligned in a plane substantially parallel to that of said anode, a substantially planar grid supported in A spaced opposing relation to both said anode and said cathode and on the opposite side of said cathode from said anode, and electron-emissive coatings only on the sides of said cathode members which are exposed to said control electrode.

6. A vacuum tube comprising, a cathode having an electron-emissive surface, an anode of generally hyperbolic configuration consisting of anode surface portions which are substantially unexposed to said cathode-emissive surface, means supporting said anode in spaced relation to said cathode with the plane-of symmetry of said anode surface portionssubstantially including the axis of said cathode, and a control electrode supported in spaced opposing relation to both said anode and said cathode and outside of the space current path therebetween.

'7. A vacuum tube comprising, a cathode having an electron-emissive surface, an anode of generally hyperbolic configuration consisting of anode surface portions which are substantially unexposed to said cathode-emissive surface, means supporting said anode in spaced relation to said cathode with the plane of symmetry of said anode surface portions substantially including the axis of said cathode, a control electrode having a surface of generally hyperbolic configuration, and means supporting said control electrode in spaced relation to both said anode and cathode with the plane of symmetry of said control-electrode surface substantially including the axis of said cathode. I

8. A vacuum tube comprising, a cathode having an electron-emissive surface, a pair of anodes each of generally hyperbolic configuration and each consisting of anode surface portions which are substantially unexposed to said cathodeemissive surface. means supporting said anodes in spaced relation to said cathode and on opposite sides thereof with the planes of symmetry of said anode surface portions substantially coincident with each other and including the axis of said cathode, a pair of control electrodes each having a surface of generally hyperbolic configuration, and means supporting said control electrodes in spaced relation to said cathode and on opposite sides thereof with the planes of symmetry of said control-electrode surfaces substantially coincident with each other, substantially normal to those of said anodes, and including the axis of said cathode.

9. A vacuum tube comprising, a cathode having an electron-emissivesurface over only a portion of the area thereof, a planar anode, means supporting said anode with the plane thereof substantially including the axis of said cathode, and.

a control electrode supported in spaced opposing relation to both said anode and said cathode and outside of the space current path therebetween.

10. A vacuum tube comprising, a cathode having an electron-emissive surface over only a portion of the area thereof, a planar anode, means supporting said anode with the plane thereof substantially including th axis of said cathode, and a planar control electrode supported in spaced opposing relation to both said anode and cathode with the plane of said control electrode substantially parallel to the plane of said anode.

11. A vacuum tube comprising, a cathode having an electron-emissive surface over only a portion of the area thereof, 'a pair of planar anodes supported in spaced relation to said cathode and on opposite sides thereof with the planes of said anodes substantially coincident with each other and including the axis of said cathode, and a pair of planar control electrodes supported in spaced opposing relation to said cathode and on opposite sides thereof with the planes of said control electrodes substantially parallel with each other and with theplane of said anodes.

RUDOLF c. HERGENROTHER. 

